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Add unsafe blocks in unsafe Thread::new

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This commit is contained in:
Chris Denton 2024-07-16 20:48:39 +00:00
parent 55c84e39cc
commit 10b845cbc8
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1 changed files with 17 additions and 13 deletions
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30
library/std/src/sys/pal/windows/thread.rs
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@ -22,28 +22,30 @@ pub struct Thread {
impl Thread {
// unsafe: see thread::Builder::spawn_unchecked for safety requirements
#[allow(unsafe_op_in_unsafe_fn)]
// FIXME: check the internal safety
pub unsafe fn new(stack: usize, p: Box<dyn FnOnce()>) -> io::Result<Thread> {
let p = Box::into_raw(Box::new(p));
// CreateThread rounds up values for the stack size to the nearest page size (at least 4kb).
// If a value of zero is given then the default stack size is used instead.
let ret = c::CreateThread(
ptr::null_mut(),
stack,
Some(thread_start),
p as *mut _,
c::STACK_SIZE_PARAM_IS_A_RESERVATION,
ptr::null_mut(),
);
let ret = HandleOrNull::from_raw_handle(ret);
// SAFETY: `thread_start` has the right ABI for a thread's entry point.
// `p` is simply passed through to the new thread without being touched.
let ret = unsafe {
let ret = c::CreateThread(
ptr::null_mut(),
stack,
Some(thread_start),
p as *mut _,
c::STACK_SIZE_PARAM_IS_A_RESERVATION,
ptr::null_mut(),
);
HandleOrNull::from_raw_handle(ret)
};
return if let Ok(handle) = ret.try_into() {
Ok(Thread { handle: Handle::from_inner(handle) })
} else {
// The thread failed to start and as a result p was not consumed. Therefore, it is
// safe to reconstruct the box so that it gets deallocated.
drop(Box::from_raw(p));
unsafe { drop(Box::from_raw(p)) };
Err(io::Error::last_os_error())
};
@ -51,7 +53,9 @@ impl Thread {
// Next, reserve some stack space for if we otherwise run out of stack.
stack_overflow::reserve_stack();
// Finally, let's run some code.
Box::from_raw(main as *mut Box<dyn FnOnce()>)();
// SAFETY: We are simply recreating the box that was leaked earlier.
// It's the responsibility of the one who call `Thread::new` to ensure this is safe to call here.
unsafe { Box::from_raw(main as *mut Box<dyn FnOnce()>)() };
0
}
}